Endodontic instruments

ABSTRACT

A method of manufacturing endodontic instruments is disclosed. Each of the instruments includes a substantially non-cutting pilot portion, a relatively short working portion, and a flexible shank portion which is of a substantially smaller average circumferential span than the working portion. The working portion of the instrument has a maximum circumferential span larger than that of the blank from which it is made. The instrument may have a handle at its distal end for manual manipulation, or may be adapted for attachment to a mechanical handpiece. The non-cutting pilot, the short length of the working portion, and the flexibility of the shank combine to allow the instrument to be used in curved root canals without causing undue change in the natural root canal contours.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 60/732,367 entitled “Endodontic Instrument” filed Nov. 1,2005; U.S. Provisional Patent No. 60/732,047 entitled. “EndodonticInstrument” filed Nov. 1, 2005; U.S. Provisional Patent Application No.60/732,631 entitled “Endodontic Instrument” filed Nov. 1, 2005; and U.S.Provisional Patent Application No. 60/732,039 entitled “TreatedEndodontic Instrument” filed Nov. 1, 2005 the entire contents of whichare incorporated by reference.

FIELD OF THE-INVENTION

This invention relates to endodontic instruments and a method formanufacturing endodontic instruments in general. More specifically, thisinvention relates to endodontic instruments for use in root canal dentalprocedures.

BACKGROUND OF THE INVENTION

Both circulatory and neural support for a tooth enters the tooth at theterminus of each root. During a root canal operation, any diseased pulptissue in the root canal is extracted using endodontic files and reamersthat are generally tapered. These instruments generally have workingsurface or portions along the major portions of the file. Since the rootcanals are small, curved and calcified, the instruments used have towithstand high torsional stresses during such removal process so as notto complicate the treatment by breaking.

The endodontic files and reamers used to clean out and shape the rootcanal are rotated and reciprocated in the canal by dentists, eithermanually or with the aid of dental handpieces onto which the files aremounted. Files of increasingly larger diameters are generally used insequence in order to achieve the desired cleaning and shaping.

Many endodontic instruments used for this operation have torsionallimitations. Some of the improved ones are disclosed in U.S. Pat. Nos.4,538,989, 5,464,362, 5,527,205, 5,628,674, 5,655,950, 5,762,497,5,762,541, 5,833,457, 5,941,760, and 6,293,795, the contents of theseare incorporated herein by reference. Some of these patents teachendodontic files made with an alloy of nickel/titanium containing morethan 40% titanium.

The files and reamers also have varying designs of cutting edges andsome of these designs are disclosed in U.S. Pat. Nos. 4,299,571,4,332,561, 4,353,698, 4,457,710, 4,661,061, 4,850,867, 4,904,185,5,035,617, 5,067,900, 5,083,923, 5,104,316, 5,275,562, 5,735,689,5,902,106, 5,938,440, 5,980,250, 6,293,794, and 6,419,488, 6,428,317,and Patent Application Publication Nos. US2002/0137008 A1, andUS2004/0023186 A1, incorporated herein by reference. These files haveworking portions spanning the lengths of the shanks and include helicalcutting surfaces.

SUMMARY OF THE INVENTION

The present invention relates to a method of manufacturing an endodonticinstrument or a set of endodontic instruments, the instrument includinga pilot portion at its proximal end, a relatively short working portion,and a flexible non-working shank portion towards its distal end that isof a substantially smaller average circumferential span than the workingportion. The working portion may be towards the proximal end or towardsthe mid-portion of the instrument.

According to one embodiment of the invention, a method for manufacturingan endodontic instrument includes:

providing a blank having a longitudinal axis and a circumferential spanthat is the same as that of a non-working shank of the instrument;

positioning at least a portion of each of said blank away from thenon-working shank adjacent a die having walls defining at leastpartially the shape and circumferential span of a working portion of theinstrument;

compressing said blank against said walls of said die with a forcesufficient to deform said blank into a shape reflecting said walls ofsaid die to form a working portion;

forming a pilot portion near the end of the instrument adjacent theworking portion; and

treating at least a portion of the instrument including at least aportion of the shank, the working portion, the pilot portion orcombinations thereof;

wherein said working portion has a circumferential span substantiallylarger than the circumferential span of the blank.

In one embodiment, at least a portion towards the proximal end of thenon-working shank has substantially the same circumferential span asthat of the blank. In another embodiment, the entire length of the shankmay have a substantially smaller circumferential span than that of theblank. In a further embodiment, the shank may be tapered towards theproximal portion. In yet another embodiment, the shank may have aportion having a reduced circumferential span towards the proximal endto create a weak point.

In one aspect, the treatment includes coating, sandblasting, anodizing,ion implantation, etching, electro-polishing, heat setting, cryogenictreatment, or combinations thereof.

In one embodiment, the treatment may be performed after the instrumenthas been formed. In another embodiment, the treatment may be performedprior to the compression process. In a further embodiment, the treatmentmay be performed when the blank is manufactured.

In a further aspect, the instrument or blank may have a coating forimproving durability, and/or lubricity and/or improving cuttingefficiency and/or strength.

-   -   Some treatment methods may also impart a different color to the        treated portions. These colored working portions may serve as        wear indicators.

According to another embodiment of the invention, the method includes:

-   -   providing a set of blanks for making instruments, all the blanks        having an identical circumferential span;    -   positioning at least a portion of each said blank next to a        non-working shank portion adjacent a die having walls defining        at least partially the shape and circumferential span of a        working surface of the instrument;    -   compressing at least a portion of each of said blank against        said walls of said die with a force sufficient to deform said        wire into a shape reflecting said walls of said die to form the        working portion; and    -   forming a pilot portion near the end of each of the blank close        to the working portion;        wherein the shank portion of each of the instruments in the set        is of substantially the same circumferential span as the blank        and each working portion has a different circumferential span.

In The present invention further relates to method of manufacturing aset of endodontic instruments including:

providing a set of blanks, each having a distal end and a proximal end,said blanks having varying circumferential spans that are of the samecircumferential spans as non-working shank portions of the respectiveinstruments made from them;

positioning at least a portion of each said blank next to thenon-working shank portion adjacent a die having walls defining at leastpartially the shape and circumferential span of a working surface of adental instrument;

compressing at least a portion of each of said blank against said wallsof said die with a force sufficient to deform said wire into a shapereflecting said walls of said die to form a working portion; and

forming a pilot segment near an end of each of the blank close to theworking portion;

wherein each blank produces one instrument in the set having a workingportion with a predetermined circumferential span that is different fromthat of the other instruments in the set.

In one aspect, the compression force may be adjusted so that thethicknesses of the working surfaces in the set of instruments aresubstantially the same, even though the circumferential spans of theworking surfaces are different.

According to yet a further embodiment of the invention, a method formanufacturing a set of groups of endodontic instruments includes:

providing a set of groups of blanks, the set and groups each having afinite number of blanks, wherein each blank having a circumferentialspan, and each group having a different circumferential span from othergroups in the set, and one portion of each blank forms the non-workingshank of the instrument;

positioning at least a portion of each blank next to the non-workingshank adjacent a die having walls defining at least partially the shapeand circumferential span of a working portion of the instrument;

compressing said blank against said walls of said die with a forcesufficient to deform said blank into a shape reflecting said walls ofsaid die to form a working portion; and

forming a pilot portion near the end of the instrument close to theworking portion;

wherein each said working portion has a circumferential spansubstantially larger than the circumferential span of the blank, and theworking portion of one instrument in the group has a differentcircumferential span and thickness from the others in the same group.

In one the thickness of the working portion of an instrument in onegroup may be the same as an instrument in another group of the set. Inanother embodiment, the thickness of the working portion of aninstrument in one group may be the same as an instrument in every othergroup in the set. In a further embodiment, the thickness of the workingportion of all instruments in the set may be different.

In one aspect, the number of groups is fewer than number of instrumentsin the set. In another aspect, the number of groups is one.

According to one embodiment, at least two instruments in the set may beproduced from each group of blanks. According to another embodiment, atleast three instruments in the set may be produced from each group ofblanks. In one aspect, the working surface of each of the otherinstruments in the set produced from the same group of blanks has amaximum circumferential span and thickness smaller or larger than thecircumferential span of the other instruments in the group of the set.

In one aspect, the set of blanks may be provided in a spool. In anotherrespect, the set of blanks may be individual severed pieces.

In one embodiment, at least a portion of each of the instruments in theset including at least a portion of the shank, the working portion, thepilot portion or combinations thereof, may be treated. The treatment mayinclude coating, sandblasting, anodizing, ion implantation, etching,electro-polishing, heat setting, cryogenic treatment, or combinationsthereof. In one embodiment, the treatment may be performed after theinstrument has been formed. In another embodiment, the treatment may beperformed prior to the compression process. In a further embodiment, thetreatment may be performed when the blank is manufactured.

In one embodiment, the working portion of any of the embodimentsmentioned above may include at least one projecting section, eachprojecting section extending beyond a radius and defining an apex, andincluding a leading portion extending forward of the apex and making anangle with the longitudinal axis of the shank of less than about 90° anda trailing edge portion extending rearward of the apex and making anangle of less than about 90° with longitudinal axis of the shank. Theapex of the projecting portion defines a point of maximum dimension orcircumferential span of the working portion.

In another embodiment, the walls of the die may be configured to produceat least one projecting section, each projection section liessubstantially in the plane of the flattened working portion.

In a further embodiment, each projecting section does not twist aboutthe longitudinal axis of the shank portion more than 359 degrees. In yeta further embodiment, the projections do not intersect each other or thelongitudinal axis of the working portion.

In one embodiment, a portion of the blank may be positioned adjacent thewalls of the die for compression. In another embodiment, the walls ofthe die may be positioned against the portion of the blank chosen to becompressed.

The present invention also relates to an endodontic instrumentincluding:

a relatively short working portion having a proximal end, a distal endand including at least one projecting section;

a pilot portion adjacent the proximal end of the working portion; and

a flexible shank portion adjacent the distal end of the working portion,a portion of said flexible shank is of a substantially smaller averagecircumferential span than the working portion;

wherein at least a portion of the shank, the working portion, the pilotportion, or combinations thereof has been treated.

The configuration of the working portion of the instrument may includeany of those configurations mentioned above.

The present invention still further relates to set of endodonticinstruments, each including an instrument having:

a relatively short working portion having a proximal end, a distal endand including at least one projecting section;

a pilot portion adjacent the proximal end of the working portion; and

a flexible shank portion adjacent the distal end of the working portionand having a longitudinal axis, at least a portion of the shank portionhas a substantially smaller average circumferential span than theworking portion, and has a different circumferential, span from that ofany other instrument in the set;

a wherein the thickness of each of the working portions in the set ofinstruments is substantially the same as that of others in the set, andthe circumferential span of one working portion is different from thatof others in the set.

The present invention yet still further relates to a set of groups ofendodontic instruments, each instrument having:

a relatively short working portion;

a pilot portion; and

a flexible shank portion having a longitudinal axis, at least a portionof the shank portion has a substantially smaller average circumferentialspan than the working portion, and has a different circumferential spanfrom that of instruments in other groups;

wherein the thickness and circumferential span of one of the workingportions in the groups are different from those of others in the group.

In one embodiment, the thickness of the working portion of oneinstrument in one group in the set may be the same as the thickness ofanother instrument in a different group of the set. In anotherembodiment, the thickness of the working portion of one instrument fromeach group in the set is identical. In a further embodiment, thethicknesses of the working portion of all the instruments in the set aredifferent.

In one aspect, at least a portion of each of the instruments includingthe shank, the working portion, the pilot portion or combinationsthereof has been treated, as noted above. The treatment includescoating, sandblasting, anodizing, ion implantation, etching,electro-polishing, heat setting, cryogenic treatment, or combinationsthereof.

In one embodiment, the treatment may be performed after the instrumenthas been formed. In another embodiment, the treatment may be performedprior to the compression process. In a further embodiment, the treatmentmay be performed when the blank is manufactured.

In one aspect, the working portion may have any of the configurations ofany of the above embodiments.

Compression as described above may include coining, stamping, coldpressing, molding or casting. While coining, stamping, cold pressing maybe operated at ambient temperature or higher, molding or casting may beperformed at elevated temperatures.

In another aspect, any of the above described instruments may have ahandle at its distal end for manual manipulation. In another aspect, theinstrument may be adapted for attachment to a mechanical handpiece,including a rotary or a vibratory handpiece.

One end of the shank portion adapted for attachment to a handle portionmay be treated. The treatment may improve the attachment strength andminimize separation of the shank portion from the handle portion.

The substantially non-cutting pilot, the short length of the cuttingsegment, and the flexibility of the shaft combine to allow theinstrument to be used in curved root canals without causing undue changein the natural root canal contours.

The blank may have a substantially spherical, a substantiallyrectangular, a substantially triangular, or a substantially ellipticalcross-section.

In one embodiment, the pilot portion may be a non-cutting portion. Inanother embodiment, the pilot portion may include abrasive surfaces. Inyet another embodiment, the pilot portion may be a continuous extensionof the working portion.

In one embodiment, the pilot portion may be about the same length as theworking portion. In another embodiment the pilot portion may be anextension at the end of the working portion.

The present invention together with the above and other advantages maybest be understood from the following detailed description of theembodiments of the invention illustrated in the drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art endodontic instrument;

FIGS. 2, 2 a, 2 b, 2 c and 2 d each show a top view, and FIG. 2 d 1shows a front view of embodiments of an endodontic instrument made withmethods according to the present invention;

FIG. 3 shows a perspective view of FIG. 2;

FIG. 3 a and 3 b each show a perspective view of an embodiment of anendodontic instrument having a different configuration for the workingportion;

FIGS. 3 c and 3 d each shows an embodiment of an endodontic instrumentof the present invention having a predetermined weak point or portionalong the shank portion;

FIG. 4 shows a group of a set of instruments of the present invention,each instrument having a different diameter shank portion and adifferent circumferential span working portion having the samethickness;

FIG. 4 a shows a group of a set of instruments of the present invention,each instrument having the same diameter shank portion, a differentcircumferential span working portion having a different thickness;

FIGS. 5, 5 a and 5 b show an instrument of the present invention havinga handle attached thereto;

FIG. 6 shows a block diagram of an exemplified process useful for thepresent invention;

FIG. 6 a is a side view of the compression process of the presentinvention as exemplified in FIG. 6;

FIG. 6 b shows a top view of the compression process of the presentinvention as exemplified in FIG. 6;

FIG. 7 shows schematic diagram of a portion of an apparatus useful forpracticing the process and making an instrument of the presentinvention;

FIG. 7 a shows a schematic diagram of another portion of an apparatusfor making an instrument of the present invention;

FIG. 7 b shows the configuration of a die useful for making aninstrument of the present invention;

FIG. 7 c and d show the side and top views respectfully of two pairs ofmolds for compressing the blank.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of the presently exemplifiedembodiments of dental instruments or tools in accordance with thepresent invention, and is not intended to represent the only forms inwhich the present invention may be constructed or utilized.

The description sets forth the features and the processes forconstructing and using the dental tools or instruments of the presentinvention in connection with the illustrated embodiments. It is to beunderstood, however, that the same or equivalent functions andstructures may be accomplished by different embodiments that are alsointended to be encompassed within the spirit and scope of the invention.

The field of endodontics involves diseases of the tooth pulp, commonlyknown as a root canal, and typically requires the dentist to removeinfected material from within the pulp of the tooth. The root canalitself is the space within the tooth that carries the blood supply intothe tooth and contains the pulp, as noted before. Within the root canalthe pulp contains the nerve endings, which causes pain to warn when onebites down too hard on a hard object. From time to time, this space (theroot canal) becomes infected and requires the dentist to clean (ream)out the root canal space in order to remove the pulp and/or otherinfected material. The better designed the instrument, the moreefficient the cleaning process.

An endodontic instrument 12 in accordance with the present invention maybe used in a root canal procedure. Some exemplary configurations may befound in U.S. Pat. No. 4,850,867, and U.S. publication No. 20020182565,U.S. Pat. No. 7,094,055, WO2002/093265, the contents of which areincorporated herein by reference.

Traditional instruments typically include long, tapered working portionshaving helical flutes along the entire length of the working portion,such as shown in FIG. 1. These instruments are typically made bygrinding a cylindrical wire. Such long working portions also mean morecontact area between the root canal and the instrument, thus subjectingthe instrument to higher torsional forces during operation.

An endodontic instrument of the present invention has a relatively shortworking portion 22, such as exemplified in FIG. 2, 2 a, 2 c, 2 d, 3, 3a, 3 b, 3 c, 3 d, 4, or 4 a. The short working portion 22 may lead tosmaller areas of contact with the root canal than traditionalinstruments. The smaller areas may result in lower torsional forces onthe instrument during use. The shorter working portion 22 also mayprovide the dentist with substantially improved control over wherecutting of dentin occurs and therefore causes much less unintendedcutting of dentin and change of the natural curvature.

An endodontic instrument 12 of the present invention, such asexemplified in FIG. 2, 2 a, 2 b, 2 c, 2 d, 3, 3 a, 3 b, 3 c, 4 or 4 a,has a relatively long non-working shank 16, having a proximal end 16 aand a distal end 16 b. The cross-section of the shank 16 substantiallycorresponds to that of the blank 30 from which the instrument 12 ismade. Substantially no grinding is performed on the shank portion 16 toform the endodontic instrument 12 of the present invention.

The shorter working portion 22 also may provide the dentist withsubstantially improved control over where cutting of dentin occurs andtherefore causes much less unintended cutting of dentin and change ofthe natural curvature.

The blank 30 may be of a substantially circular, a substantially square,a substantially rectangular, a substantially triangular, or asubstantially elliptical cross-section. Hence the shank 16 may have anyof these cross-sections.

An instrument 12 of the present invention includes a shank 16 having asmall circumferential span or diameter over a major portion of itslength, as shown in FIGS. 2, 2 a, 2 b, 2 c, 2 d 3, 3 a, 3 b, 3 c, 3 d, 4and 4 a. The small circumferential span or diameter of the shank 16 ofthe present invention makes the instrument 12 more flexible. Thisflexibility allows the instrument 12 to follow the curve of a canal moreeasily.

The shank portion 16 is also substantially longer than the workingportion 22. A traditional instrument, by contrast, has a very shortshank portion, if any. The length of the shank portion 16 provides foran instrument 12 that may bend more readily as it encounters any changein direction in the channel of the tooth.

The instrument 12 also has a substantially non-cutting pilot portion 10towards the proximal end 20 of the working portion 22, as shown in FIG.2. The substantially non-cutting pilot portion 10, the short length ofthe working portion 22, in addition to the length and flexibility of theshank 16, all combine to further allow the instrument 12 of the presentinvention to more easily follow the natural curvature of the entire rootcanal without causing undue change in the natural root canal contours.It also opens up more choices for materials that may be suitable forconstructing the instrument 12, including materials that may not besuitable for traditional instruments, materials that are nottraditionally considered as having high degrees of flexibility, ormaterials having improved strength. Such improvements may be introducedthrough treatments such as cryogenic treatments, heat setting orcombinations thereof.

Such treatments for improved strength, which may introduce acorrespondingly undesirable loss in flexibility of the blank sometimes,may still generate blanks that are suitable for the present inventionbecause of the configuration of the instrument 12 of the presentinvention.

Also, since substantially no grinding is typically performed on theshank portion 16, as mentioned above, no weak points along the shank 16are introduced by the manufacturing process. This also makes the use ofblanks 30 having smaller circumferential spans or diameters possible,and further adds to the flexibility of the instrument 12.

The blank 30 may include a titanium alloy such as nickel-titanium alloy,titanium-nitride alloy, titanium-aluminum-vanadium alloys or similar;stainless steel; silver and silver alloys; aluminum; any amorphousmetals; or a similar metal that is amenable to being drawn into a blankof small diameter or circumferential span or a wire-like form. For atitanium alloy, the amount of titanium may be present at, for example,at least about 25% by weight, more for example, may be present at, forexample, at least about 50% by weight. The nickel-titanium alloys mayalso include impurities such as C, O, N, Co, Cr, Zr, Hf, Nb, Pt, Pd. V,Fe or mixtures thereof. Fe may also strengthen and improve ductility ofthe alloy. These blanks may be made into endodontic instruments 12having good torsional resistance and good flexibility.

A suitable non-metal may also be used and may include a polymeric alloysuch as ULTEM®, which is an amorphous thermoplastic polyetherimide,Xenoy® resin, which is a composite of polycarbonate andpolybutyleneterephthalate, Lexan® plastic, which is a copolymer ofpolycarbonate and isophthalate terephthalate resorcinol resin (allavailable from GE Plastics); liquid crystal polymers, such as anaromatic polyester or an aromatic polyester amide containing, as aconstituent, at least one compound selected from the group consisting ofan aromatic hydroxycarboxylic acid (such as hydroxybenzoate (rigidmonomer), hydroxynaphthoate (flexible monomer), an aromatic hydroxyamineand an aromatic diamine, (exemplified in U.S. Pat. Nos. 6,242,063,6,274,242, 6,643,552 and 6,797,198, the contents of which areincorporated herein by reference), polyesterimide anhydrides withterminal anhydride group or lateral anhydrides (exemplified in U.S. Pat.No. 6,730,377, the content of which is incorporated herein byreference); any or combinations thereof.

The blank 30 may be present in a continuous spool. When the blank 30 isin a spool, it may undergo a straightening process prior to being cutand/or ground. For a blank of nickel-titanium alloy, the straighteningprocess is not needed as the winding process does not impart a permanentmemory to the blank.

In one embodiment, the blank 30 may be cut into the needed dimensionprior to feeding the blank 30 through the instrument manufacturingprocess. In another embodiment, the blank may be fed through theinstrument manufacturing process prior to being cut into the requireddimension.

An instrument 12 typically has a length of about 30 mm (1.2 inches), andhas a proximal end adapted to be mounted to a conventional handle 25, asshown in FIG. 5, or a rotary handle 25, as shown in FIGS. 5 a and 5 b.The conventional handle 25 may be adapted for manual cutting of the rootcanal. The rotary handles 25 may be adapted for mounting to a mechanicalhandpiece, such as a rotary handpiece or vibratory handpiece.

The shank portion 16 may be cylindrical, as shown in FIGS. 2 and 3, ormay be of any other cross-section mentioned above, and may have acircumferential span or diameter of between about 0.2 to about 0.8 mm(0.01 and 0.03 inches).

Typical lengths of shank portion 16 ranges from, for example, 1.0 mm to100 mm, more for example, 10 mm to 50 mm, while the typical workingportion 22 ranges from, for example, 0.25 mm to 10 mm, more for example,1.5 mm to 3.0 mm, even more for example, up to about 14 mm (0.5 inches).

In one embodiment, the working portion 22 may be substantially in oneplane. In another embodiment, the working portion 22 may haveprojections that are out of plane.

In one embodiment, the working portion 22 may be made to be slightlytapered towards the pilot portion 10. In a further embodiment, theworking portion 22 may be slightly tapered towards the shank portion 16.In another embodiment, the working portion 22 may be slightly taperedtowards both the pilot end 10 and the shank portion 16, as shown, forexample, in FIGS. 2, 2 a, 2 b, 2 c, 2 d, 3, 3 a, 3 b, 3 c, 3 d, 4, and 4a. Any or all of these illustrates embodiments of an endodonticinstrument 12 which may be fabricated in accordance with the presentinvention.

The working portion 22 of the instrument 12 may be flat, orsubstantially in one plane, and having a thickness, as shown in FIGS. 3,3 a, 4 and 5. In one embodiment, the flattened working portion 22 mayvary in thickness, from a thinner edge to a thicker central portion. Inanother embodiment, the thickness of the working portion 22 may besubstantially uniform.

In another embodiment, the working portion 22 may have projections thatare out of plane or may be of a wedge-like sections or projections 18that are not helically wound with respect to the longitudinal axis ofthe shank 16, as exemplified in FIGS. 2 a, 2 d, 3, 3 a, and 4. Theprojecting section 18 extends beyond radius R of the shank 16 asmeasured perpendicular to the longitudinal axis. One or more of theseprojections 18 may be straight, radiating outward about the workingportion 22 in one plane, as shown in FIG. 2 a.

In FIG. 2 a, there is a pair of oppositely located projecting sections18. In other embodiments, more than one pair of projecting sections 18,each extending beyond the radius of the shank 16 may be possible, asshown in FIG. 2 d.

In one embodiment, as shown in FIG. 2 a, at least one of thesewedge-like projections 18 may have a radius R and an apex A and includesa leading portion 24 a extending forward of the apex A and making anangle with the longitudinal axis of less than about 90°, and a trailingedge portion 20 a extending rearward of the apex and making an angle ofless than about 90° with the longitudinal axis. In one aspect, thewedge-like projections 18 including the forward and trailing portions 20a and 24 a that are typically at an oblique angle to the longitudinalaxis.

In another embodiment, each projecting section 18 may not be straight,but may twist about the longitudinal axis of the shank portion 16 notmore than 359 degrees, as shown in FIG. 3 a.

In yet another embodiment, the projections 18 may be straight ortwisted, and do not intersect each other, such as a spade type drill,having a working portion 22 with a plurality of flutes or wedge shapedportions 18 extending beyond the diameter of the shank 16, one of whichis in 3 b.

In one embodiment, the working portion 22 may have a uniform thickness.In another embodiment, the thickness may vary from a thinner edge to athicker central portion. The thinner outer surface 18 of the workingportion 22 may have better cutting efficiency.

Referring to FIGS. 2 and 2 a, 2 cand 2 d, the working portion 22 mayhave a slight taper present at both ends of the working portion 20 and24, as shown. The tapering makes the largest circumferential spansection not towards either one of the ends 20 and 24, but either aboutthe mid-section of the working portion 22, or off the mid-section of theworking portion 22, as shown in FIGS. 2, 2 a, 2 b, 2 c, 2 d, 3, 3 a, 3b, 3 c, 3 d, 4 and 4 a.

The working portion 22 may also be suitably tapered in three portions. Afirst transition portion 20 increases in circumferential span from thedistal end or portion of the pilot portion 10 until it meets the mainbody of the working portion 22. The main body portion then decreases incircumferential span towards its distal end or portion 24, but may be ata larger slope of decrease than the slope of increase from its proximalend or portion 20 towards the main body. The main body of the workingportion 22 connects at its distal end or portion 24 to the shank portion16. Other embodiments are possible, including a reverse taper wherebythe proximal end or portion diameter of the working portion 22 may begreater than the distal end or portion diameter, or any othercombination.

In the embodiments as exemplified in FIGS. 2, 2 a, 2 b, 2 c, 2 d, 3, 3a, 3 b, 4 and 4 a, the non-working shank 16 is of a substantiallycylindrical shape and has a proximal end 16 a and a distal end 16 b. Inother embodiments, shanks 16 having other cross-sectional shapes, suchas a triangle, a square or a rectangle, may also be contemplated.

The tapered end 24 of the working portion 22 is contiguous with thedistal end 16 b of the non-working shank 16. The working portion 22first widens then reaches an apex A, then narrows until it reaches thediameter of the shank 16. The projections or wedges 18 are seen, in FIG.2 d, to first become thinner until they reach a minimum at apex A thenthicker until they reach a thickness equal to the diameter of the shank16.

In one embodiment, the tapered end 24 may be tapered such that at thepoint of joining with the distal end 16 b of the non-working shank 16,there is a matching of diameters. In another embodiment, the distal end16 b is of a slightly larger diameter than the narrow portion of thenon-working shank 16 so that there is a smooth transition from thetapered end 24 of the working portion 22 towards the non-working shank16. In a further embodiment, the proximal end of the non-working shank16 may have a slightly larger diameter than working portion 22.

FIG. 2 d shows a side elevational view of an embodiment of an instrument12 of the present invention having four fluted or wedge shapedprojections 18 radiating outward from the axis of the shank 16. In FIG.2 d, the two pairs of projecting sections 18 form a square-shape form ora parallelogram. The cross-section of one is exemplified in FIG. 2 d 1.

FIG. 3 is a perspective view of the embodiment of FIG. 2, showing thethickness of the working portion 22. As shown, the thickness of theworking portion 22 is substantially uniform. In other embodiment, thethickness may vary throughout the working portion 22, as noted above.The thickness of the working portion 22 may be determined by thecircumferential span, or diameter of the blank 30 used, theconfiguration of the die, and the circumferential span of the resultingworking portion 22.

In one embodiment, when using blanks 30 having, for example, the samediameter or circumferential span, to make a series of instruments 12having different circumferential span working portion 22, the thicknessof the working portions 22 varies, such as shown in with a group of setin FIG. 4 a. The working portions 22 have substantially uniformthicknesses throughout the structure. In FIG. 4 a, the shank portions 16are of one diameter in the group, while the working portions 22 vary incircumferential spans in the group. As shown, the working portions 22have different thicknesses. In this embodiment, the need to stock blanks30 with varying diameters or circumferential spans may be eliminated.

In another embodiment, as exemplified in FIG. 4, a group of a set ofinstruments 12 of the present invention is made from blanks 30 havingdifferent diameters or circumferential spans, resulting in shankportions 16 having different diameters. In this embodiment, thethicknesses of the working portions 22 within a group are the same whilethe circumferential spans of the working portions 22 within a groupvary. In some embodiments, as illustrated in FIG. 4, the thickness ofthe working portion 22 of a single instrument 12 may be constant. Inother embodiments, the configuration of the die may be varied to producea varied thickness of working portion 22 of a single instrument 12 (notshown). In still other embodiments, the circumferential spans and thethicknesses of the working portions 22 of the group of a set ofinstruments 12 may vary in a manner similar to that illustrated in FIG.4 a while using blanks 30 of different diameters or circumferentialspans.

The thickness of the working portion 22 in a group may be optimized forcutting efficiency, ease of manufacture, or decreased likelihood offracture during use.

In some embodiments, the length of the working portion 22 may also varyin addition to the circumferential span and configuration. However, incontrast to prior art instruments, the length of the working portion 22does not exceed the length of the shank portion 16 such that theinstrument 12 may preserve its flexibility.

A pilot portion or tip 10 guides the flexible shank 16 within the canal.The pilot portion 10 is substantially non-cutting and may have adiameter small enough to allow an instrument 12 to enter the apical areaof the root canal of a human tooth and to act as a guide to follow thecanal to the apex. Thus, the purpose of the pilot portion 10 istherefore to guide the instrument 12, and not necessarily to perform anycutting. In one embodiment, the pilot portion 10 may be a non-cuttingportion. In some embodiments, the substantially non-cutting portion mayinclude an abrasive surface. The abrasive surface may be impartedthrough coating, sandblasting, anodizing, ion implantation, etching,electro-polishing or combinations thereof, as further discussed below.In still other embodiments, the pilot portion 10 may have raised edgesor other projections on its surface, as long as they do not cause thepilot portion 10 to have a substantial cutting effect.

The length of the pilot portion 10 may also vary, and may be, forexample, between about 0.01 and 14 mm long, more for example betweenabout 0.75 and 3 mm.

The pilot portion 10 may be tapered (as shown in FIG. 2 c) or nontapered(as shown in FIG. 2 b). If tapering is used in the pilot portion 10, itwill usually increase in diameter from its proximal end to its distalend is also shown in FIG. 2 c.

In FIGS. 2 and 2 a, the pilot portion 10 is a short portion extendingfrom the end 20 of the working portion 22. As shown, the pilot portion10 is a smooth tapered cylinder with a blunt proximal end. In otherembodiments, the pilot portion 10 may have rounded (bullet shaped) ends,as exemplified in FIG. 2 c.

In FIG. 2 or 2 a, the pilot portion 10 is present as a slight extensionor a stump at the end 20 of the working portion 22. This may be rounded,and may be generated by grounding or polishing the working end 20.

In FIG. 2 b, the pilot portion 10 is almost of the same length as thatof the working portion 22. In FIG. 2 b, the pilot portion 10 as shown isalso a smooth cylinder having a uniform circumferential span, forexample, diameter, along its length, except for the end. In otherembodiments, the pilot portion 10 may be tapered towards the end, asshown in FIG. 2 c. As shown, the end of FIGS. 2 band 2 care not rounded.In other embodiments, the end may also be rounded, such as shown inFIGS. 2 and 2 a. In this configuration when the pilot portion 10 isalmost as long as the working portion 22, the instrument 12 may beuseful a coronal shaper.

In FIGS. 2, 2 a, 2 b, 2 c, 2 d, 3, 3 a, 3 b, 3 c, 3 d or 4, thecross-section of the leading end of the pilot portion 10 a may be of asubstantially rectangular shape. In this embodiment, when the instrument12 encounters a root canal channel that is narrower than the diameter ofthe shaft used, the nose portion 10 a may begin to cut aggressively.With a more rounded nose portion 10 a, as illustrated in FIG. 2 c,the-nose portion 10 a has essentially no cutting edge.

Referring again to FIG. 4 a, a group of a set of endodontic instruments12, each made from blanks 30, where each has the same circumferentialspan or diameter. Each of the instruments 12, as shown in FIG. 4 a, hasa working portion 22 that is different in circumferential span fromanother instrument 12 in the group, and the thickness of the projectionsections 18 is also substantially different from that of anotherinstrument 12 in the group.

The present manufacturing method includes using blanks 30 that are ofthe same diameter or circumferential span, thus generating instruments12, all having shanks 16 having the same diameter or circumferentialspan, or using blanks 30 that are of different diameters orcircumferential spans, making instruments 12, all having shanks havingdifferent diameters or circumferential spans. The process isschematically shown in FIG. 6. and includes:

providing a blank 30 having a circumferential span that is substantiallysmaller than the circumferential span of the finished working portion 22of the finished instrument 12 in process 1;

forming a pilot portion 10 near the end of the instrument close to theworking portion 22 by shaping or removal of material in process 2; and

positioning at least a portion of said blank 30 adjacent a die havingwalls defining at least partially the shape and circumferential span ofa working portion 22 of a dental instrument 12 and compressing saidportion of said blank 30 against said walls of said die with a forcesufficient to deform said portion of said blank 30 adjacent the die intoa shape reflecting said walls of said die to form a working portion 22in process 3.

The pilot portion 10 may be formed by a number of methods, includinggrinding, or any other similar process, such as polishing. Details of anexemplary method may be found in U.S. Pat. Nos. 5,464,362, and5,816,807, the contents of which are incorporated herein by reference.These patents disclose the manufacture of dental drills by removing orgrinding material from the working portion 22. In the present invention,any grinding, if performed, may be used for forming the pilot portion10.

The process may further include a treatment process for treating atleast a portion of the instrument 12 including at least a portion of theshank 16, the working portion 22, the pilot portion 10 or combinationsthereof. The treatment process may be carried out after the instrument12 is formed or prior to the grinding or compression process also, asshown in dotted line in FIG. 6. The treatment process may also berepeated.

In one embodiment, the processes may be performed in any other order,including a reverse order. These processes may be carried out using anapparatus as exemplified in FIG. 7, described below.

FIG. 6 a is a side view of the compression process of the presentinvention as exemplified in FIG. 6. The blank 30 moves into the locationwhere the two parts of a die or mold M is located. The two parts closes,and in the process, compresses a portion of the blank 30 towards theproximal portion with a force F that is sufficient to deform the blankinto the shape of the walls of the die M. The blank 30 may be cut tolength, as illustrated, or inserted between two pieces of the mold as itunrolls from a spool, is placed between the two pieces of the mold.Compression force is applied as illustrated and deformation on the wireblank forces it into the shape of the finished piece. The process mayrequire one or more “hits” from one or more directions to achieve thedesired result.

FIG. 6 b shows a top view of the compression process of the presentinvention as exemplified in FIG. 6.

FIG. 7 schematically illustrates a portion of an exemplary machiningapparatus for practicing a part of the method of the present invention.The grinding process itself may be any known process, such as thatdescribed in U.S. Pat. No. 5,464,362, as noted above, the content ofwhich is incorporated herein by reference.

An instrument 12 may be made from a blank 30 having a circumferentialspan, for example, a diameter that is the same as the diameter of theshank 16. In accordance with an illustrated embodiment of the presentinvention, the blank 30 may be supplied from a continuous spool, asnoted above, and may be positioned to extend through an axial feed block32 and an indexing block 34 as shown in FIG. 7. A holding fixture 36 ispositioned to support the forward end of the blank 30 adjacent theperiphery of a rotating grinding wheel 38.

In the embodiment as shown in FIG. 7, the blocks 32, 34 may be advancedso that the blank 30 may move axially past the rotating grinding wheel36 at a speed of, for example, between about 3 to 8 inches per minute(75 mm to about 200 mm), and more for example, of not more than about 5inches (125 mm) per minute, if a blank of nickel-titanium is used. Inother embodiments, higher rotation rates may be used. Concurrently withthis axial movement, the indexing block 34 may be stationary or it mayhave a slight translational movement, for forming a short rounded pilotportion 10, such as shown in FIG. 2. In FIGS. 2 and 2 a, when the pilotportion 10 is a short portion extending from the end 24 of the workingportion 22, 2he end of the pilot portion is ground to have either arounded end, as shown in FIG. 2 b, or substantially rounded end, asshown in FIG. 2 c.

The blank 30 may move past the wheel once or more than once for formingthe pilot portion 10, and thus the blank 30 may be positioned withrespect to the wheel 38 such that the full depth of any cut is removedin a single pass or multiple passes, respectively.

The grinding wheel 38 may be rotated at a relatively slow surface speedof, for example, not more than about 3000 feet per minute, and more forexample, not more than about 2200 feet per minute. Further, the wheel 38may be composed of a relatively fine grit, which is greater than, forexample, about 200 grits, and more for example, about 220 grits. Thewheel having the above grit sizes may be fabricated from siliconcarbide. In other embodiments, diamond particles may also be used as thegrinding surfaces.

The grinding wheel may also be rotated at higher surface speeds. At thehigher speeds, more than one pass may be employed.

In some embodiments, instead of a grinding wheel, a polishing stationmay be present, to polish the end of blank 30 for forming a smooth endof a pilot portion 10.

After or before forming the pilot portion 10, the blank 30 may beadvanced to the compression station at point B, having a pair of die,188, as shown in FIG. 7 b, for forming the working portion 22. Asmentioned above, the walls of the die may be configured to any form orshape for generating various shapes of the working portion 22.

The compression process may be carried out by an apparatus similar tothat used for making a drill, but capable of handling a smallerinstrument. An exemplary instrument 12 is shown in FIG. 7 a, some of thedetails may be found in U.S. Pat. No. 6,290,439, the content of which isincorporated herein by reference.

As noted above, compressing may include coining, stamping, coldpressing, molding or casting. While coining, stamping, cold pressing maybe operated at ambient temperature or higher, molding or casting may beperformed at elevated temperatures. The compressing process may includeany or a combination of the above.

As shown in FIG. 7 a, a size stamp station 176 is shown to include asize stamp clamp 178. The arrow 41 represents the direction of advance.The stamp clamp 178 also includes a size stamp die assembly including analignment fixture 190, such as a spider, and a plurality of size stampdies 188 which are held within the alignment fixture, a cross-sectionalview is shown in FIG. 7 b. The size stamp clamp 178 may also include aclosure 192, which may be adapted to receive the size stamp dieassembly. The size stamp station 176 may also include devices, forexample, a hydraulic cylinder assembly 194 which operates under controlof a controller for urging the closure over the size stamp die assemblysuch that the size stamp dies 188 are closed about the leading end ofthe continuous blank material 30. In another embodiment, the blank mayalso be in discrete lengths.

FIG. 7 a shows an exemplary apparatus for performing this compressionprocess is set up separate from the machine for handling the blank 30and forming the pilot portion 10. In another embodiment, the compressionapparatus may be incorporated into the blank handling and grindingapparatus shown in FIG. 7.

The size stamp dies 188 as shown in FIG. 7 b may have a shape whichmatches the shape of the part to be held by the size stamp clamp 178,for example, the shape of the working portion 22 of an endodonticinstrument 12 of the present invention.

In one embodiment, when a continuous blank stock 30 is used, the blank30 may be held by the size stamp clamp 178 while the controller (notspecifically shown here) may advance the saw 198 toward the continuousblank 30 so as to cut at a location proximate the forward end of theinstrument 12, i.e., at a location proximate the pilot portion 10,thereby separating the leading part from the remainder of the continuousblank 30. The cutting station (not shown), may also include a proximitysensor, operably connected to the controller, for detecting theadvancement of the saw 198 to a predetermined position. Thereafter, thecontroller may retract the saw 198 to its initial position. In otherembodiments, blanks 30 having a discrete length may be used.

Once the continuous blank stock 30 has been cut and the controller hasretracted the saw 198, the controller may also move the saw station in adownstream direction until the saw is aligned with the rearmost orproximal portion 16 a of the shank 16 of the instrument 12. The saw maythen rotatably advance once again to cut through the continuous blankstock 30 at a location proximate the proximal end 16 b of the shank 16.

After the blank 30 has been cut to the desired size, the size stampstation 176, again under control of the controller mentioned above movesthe size stamp platform 180 in a downstream direction as indicated byarrow 41. In one embodiment, the size stamp station platform 180 may bemoved in a downstream longitudinal direction by a linear distance whichexceeds the longitudinal growth of the continuous blank stock 30 in thedownstream longitudinal direction during one sequence of formingoperations. For example, the size stamp station may be moved in adownstream longitudinal direction by the expected amount of longitudinalgrowth of the continuous blank stock 30 in the downstream direction plusa predetermined additional amount, such as 0.100 inch.

Accordingly, additional portions of the continuous blank stock 30 maynow be forged without contacting the discrete part held by the sizestamp clamp 178. Thus, the forming method and apparatus of the presentinvention may continue to process the discrete part held by the sizestamp clamp while forming additional portions of the continuous stockmaterial at the same time.

Once the size stamp station 176 has completed stamping or compressionoperations, the size stamp station 176 can eject the stamped part whichmay be directed by, for example, a chute, a conveyor or the like, into abin. In one aspect, the size stamp station may include a kicker rodwhich may be spring extended so as to eject the stamped part once thesize stamp dies 188 have been opened.

The compressing process has been described as a stamping process, but itmay also include swaging, coining, hot or cold forming, forging,pressing, molding, casting or otherwise subjected to mechanicalcompression to “flare” the portion of the blank 30 adjacent the die suchthat it is flattened in one embodiment to have a circumferential spanthat is greater than the unflattened or round portion of the blank 30and having a thickness that is smaller than the unflattened shankportion 16, as shown in FIG. 2. In one embodiment, the edges of theflattened portion may be polished, machined, sheared or further formedinto sharp cutting edges. FIGS. 7 c and 7 d show the side and top viewsrespectfully of two pairs of molds M used for compressing the blank 30,as described in the illustrated process in FIGS. 6, 6 a and 6 b. Asnoted above, the blank 30 may be of any cross sectional shape and have aparallel or tapered shape before forming.

The blank 30, which may be cut to length, as illustrated, or insertedbetween two pieces of the mold as unrolled from a spool, as discussedabove, may be placed between the two pieces of the mold.

In another embodiment, as noted above, the compression may generate aworking portion 22 having at least one projection including the forwardand trailing portions that are typically at an oblique angle to thelongitudinal axis. In another aspect, one or more of these projectionsmay be straight, radiating outward about the working portion 22 in oneplane, as shown in FIG. 2 a.

In another embodiment, each projecting section 18 may not be straight,but may twist about the longitudinal axis of the shank portion 16 notmore than 359 degrees, as shown in FIG. 3.

In yet another embodiment, the projections 18 may be straight ortwisted, provided that they do not intersect each other, as shown inFIG. 3 a.

The severed blank/instrument 12 may then be further treated, as is alsodiscussed above. The treatment may be performed on the entire instrument12 or at select portions and may include coating, sandblasting,anodizing, ion implantation, electro-polishing, etching, or combinationsthereof, as disclosed above. Any or combinations of these treatments mayserve to modify the surface properties of the instruments 12, asdisclosed above. Other treatments, including cryogenic treatment, heatsetting or combinations thereof, may serve to improve the bulkproperties, for example, the strength of the metal, polymer or alloy,by, for example, modifying the molecular structure of the base material.These may also be used in combination with the surface treatmentsmentioned above, either before or after any of the other treatments,provided that one type of treatment does not adversely change or affectthe desirable effects imparted by another type of treatment, as noted.In general, the properties least likely to be affected by othertreatment methods are performed first.

The treatments including coating, sandblasting, anodizing, ionimplantation,. electro-polishing, etching or combinations thereof, maybe performed to modify the surfaces of at least a portion of the workingportion 22, and/or the shank 16, and/or the pilot portion 10, as notedabove. The treatment may also act to remove any burrs that may formduring the process.

In addition, these surface treatments may also remove any oxidizedlayers, for example, oxide layer that may be present on the surface ofthe blank that is generated during the manufacturing process of theblank 30. The oxidized layer may be regenerated even after thetreatment, but not to the same extent as the untreated surfaces. Theremoval of the oxidized layer may also improve the cutting efficiency ofthe working portion 22.

A suitable cryogenic treatment is described in U.S. Pat. No. 6,314,743,the content of which is incorporated herein by reference. An exemplarytreatment may involve a cryogenic cycle having a cool down phase from aninitial start time, during which the blank 30 may be cooled down in adry cryogenic environment to about −300° F., over a span of betweenabout six (6) and eight (8) hours, followed by a cryogenic hold phaseduring which the blank 30 may be held at about −300° F. over betweenabout twenty-four (24) and thirty-six (36) hours, followed by acryogenic ramp up phase during which the blanks are ramped up to about−100° F. over between about six (6) and eight (8) hours. Then a firsttempering cycle having a ramp up phase may be performed, during whichstage the blank is ramped up in a dry tempering environment to about350° F. over about one-half (½) hour, followed by a hold phase duringwhich the blank 30 may be held at about 350° F. over about two (2)hours, followed by a ramp down phase to below about 120° F., but notgenerally all the way to the ambient temperature, over between about two(2) and three-and-half (3½) hours. A second tempering cycle may followwhich may have a time-temperature profile fairly comparable to the firsttempering cycle. In some methods, a third tempering cycle may beperformed.

The cryogenic ramp down phase may be arranged to have a varying rate ofdescent. For example, the descent may be steeper initially from ambientto about −100° and then more gradual thereafter for temperatures below−100° F. to about the cryogenic hold temperature of about −300° F. Thetemperature descent from the start time at ambient temperature to theabout −100° F. level may be achieved over about the first one (1) hourafter the start time, while the temperature descent from below about−100° F. to about −300° F. may be achieved over between about five (5)and seven (7) hours.

The cryogenic ramp up phase may also have a varying rate of ascent, forexample, that may correspond to an exponential decay of the cryogenichold temperature from the about −300° F. to about −100° F over betweenthe about six (6) and eight (8) hours. The exponential decay of thecryogenic hold temperature from the about −300° F. to about −100° F. mayalso include a stage when a temperature of about −200° F. is not reachedfrom the base hold temperature of −300° F. until six (6) hours into thecryogenic ramp up phase, while the remaining decay up to −100° F. occursover a next two (2) hours. In other embodiments, the exponential decayof the cryogenic hold temperature from the about −300° F. to about −100°F. may be arranged to transpire such that a temperature of about −200°F. is not reached from the base hold temperature of −300° F. untilfive-and-half (5½) hours into the cryogenic ramp up phase, the remainingdecay up to −100° F. occurring over a half (½) hour period.

In an exemplary embodiment, the cryogenic environment may be provided bya Dewar chamber and the tempering environment may be provided by aconvection oven. Accordingly, the transition between the cryogenic cycleand the first tempering cycle would entail physical transfer of theblank from Dewar chamber to the convection oven.

Typically, a hold down phase at about −300° F. may extend between abouttwenty-four (24) and thirty-six (36) hours. During this “hold phase” theblank 30 may thermally contract. If the blank 30 is made of metal or ametallic alloy, it is surmised that the microstructure re-organizesitself to become more spatially uniform. This uniformity may providestronger blanks for making the instruments 12 by decreasing the packingdensity defects.

Another cryogenic process is disclosed in U.S. Pat. No. 6,332,325,incorporated herein by reference. The process subjects an article ofmanufacture to extreme negative temperatures and cycling the articlebetween a set of negative temperatures for a number of cycles. Theprocess is completed by heating the article to an extreme positivetemperature and then allowed to cool to ambient room temperature. It isshown that this cryogenic thermal cycling process strengthens thearticle by realigning its molecular structure to eliminatemicro-cracking and other manufacturing deforming characteristics.

Other cryogenic treatment methods may be found, for example, U.S. Pat.No. 4,482,005 (Voorhees), or U.S. Pat. No. 5,259,200 (Nu-Bit, Inc.), thecontent of which is incorporated herein by reference. The Voorheespatent discloses a cryogenic cycle having ramp down and ramp up phasesflanking a wet or immersion “soaking” phase. The Voorhees discloses thatfor “tool steel”, the wet process produces an instrument 12 with longerlasting sharpness. The Nu-Bit patent discloses a quenching process byessentially dropping a target into a liquid nitrogen bath, and let setthere for the ten (10) minutes or soon, sufficient time for the liquidnitrogen to boil away. After the bath, the instrument 12 is brought backto room temperature by a jet stream of room-temperature air, making theentire process a forty minute start to finish (including the 10 minutebath) process. This quick dip method reports a gain of up to a fiftyfold (50×) improvement in drill bits. Both of these methods may have tobe modified to be practiced for blanks 30 used to make fine instrumentslike endodontic files.

The cryogenic treatment may be amenable to blanks 30 after they havebeen manufactured, for example, after they have been drawn into the formof blanks 30, other treatment process may also be amenable to beperformed during, for example, the extrusion or drawing process. Forexample, heat treatments or varying drawing speeds may be used to modifythe properties of the blanks 30, for example, to strengthen the blanks30, during their manufacturing process. For heat setting treatments, acycling between hot and cold may be employed. The rate of the heatingand cooling cycles may also be varied. Other thermal treatments mayinclude localized laser treatment. By varying the aging temperature, thedrawing or extrusion rates, the rate of heating and cooling cycles, anyirregularities in the molecular structure or molecular packing may bemodified. Multiple incremental drawing or deformation may also result inbetter uniformity and better properties than single drawing process.

Some examples of these processes may be found in U.S. Pat. Nos.4,704,329, and 6,332,325, the contents of which are incorporated hereinby reference.

While some of these treatment methods may be more amenable to blanks 30than instruments 12, they may be used for instruments 12 also, with somemodifications. For example, the method discussed in U.S. Pat. No.6,332,325 may be used to strengthen the blank 30 by realigning itsmolecular structure to eliminate micro-cracking and other manufacturingdeforming characteristics, as noted above. Therefore, though some ofthese processes have been described with respect to the blank 30, theinstruments 12 may be described in similar manners.

Coating, sandblasting, etching, anodizing, ion implantation orelectro-polishing, as noted above, may be used to modify the surface 30.For example, a micro-abrasive sandblasting device disclosed in U.S. Pat.No. 6,347,984 may be a suitable device for treating endodonticinstruments 12 of the present invention, the content of which isincorporated herein by reference. Another suitable device may be onedisclosed in U.S. Pat. No. 5,941,702, the content of which is alsoincorporated herein by reference. This exemplary device disclosed is adental air-abrading tool typically used for etching hard surfaces toenhance bond strength of adhesives, which includes a solid body havinginternally reamed passageways through which a gaseous fluid and anabrasive material are carried. A connector is mounted on one end of thebody for connecting one of the body's internal passageways to a supplyof gaseous fluid and a nozzle is mounted on the other end of the bodyfor directing the gaseous fluid to a surface. A supply of an abrasivematerial is coupled to another internal passageway of the body. Thenozzle includes an internal mixing chamber for mixing the gaseous fluidand abrasive material entering therein from the body's internalpassageways. Some slight modifications may be made to adapt it for usein the present invention

Other physical alterations of the surface such as burnishing, may alsoresult in a surface layer with reduced excess oxides.

Other exemplary treatment methods may be found in U.S. Pat. Nos.6,605,539, 6,314,743, 5,775,910, and 5,393,362, the contents of all ofwhich are hereby incorporated by reference.

Chemical etching may also be used and may be carried out in any knownprocess, including nitric acid passivation.

Ion implantation is another method that may be used, to impart changesto either small or large regions of the surface of the blank 30, forexample, to generate an amorphous surface, which may lead to increasedsurface hardness, reduced surface friction coefficient, increased wearresistance, reduced surface wetting behavior, and even an enhancement inpassivation, if desired. Ions useful for implantation may includeoxygen, nitrogen, carbon, boron, cobalt. Process conditions during ionimplantation may also be controlled to minimize hydrogen embrittlement.

When the modification is performed on the instrument 12 after theinstrument has been formed, the coating, sandblasting, anodizing, ionimplantation, etching or electro-polishing process may be performed onthe entire instrument 12 or on selected portions of the instruments 12,to modify the entire instrument. 12 or only the desired portion orportions. The process may also remove any burrs or irregularitiesgenerated during the manufacturing process while creating a modifiedsurface structure at the same time.

In addition, the surface treatments may also remove any oxidizedmaterial, for example, an oxide layer that may be present on the surfaceof the blank 30 that is generated during the manufacturing process ofthe blank 30. The oxidized layer may be regenerated even after thetreatment, but not to the same extent as the untreated surfaces. Theremoval of the oxidized layer may also improve the cutting efficiency ofthe working portion 22.

In another embodiment, after the treatment, or as the treatment process,a coating may be formed on the surface. This coating may, on the onehand, minimize the re-forming of the oxidized layer, while at the sametime provide friction reduction and/or durability enhancement, asdiscussed further below.

In a further embodiment, the existence of the oxide layer may beadvantageous in improving corrosion resistance, durability and/orfinishing of the surface. An oxide layer of titanium may, for example,impart coloring to the surface based on the thickness of the layer andmay be utilized as a wear or depth indicator. Oxide layers thicker thanan untreated passivation layer may also impart increased corrosionresistance and durability as many metal oxides are extremely hard andthicker layers may be less prone to wearing that may expose the metalsurface and lead to corrosion. Increasing the thickness of the oxidelayer may also be useful in preserving the layer when exposed toenvironments where oxygen is not available to regenerate the layer.

Coating, sandblasting, anodizing, ion implantation, etching orelectro-polishing may also modify the working surfaces 18, whetherperformed on the blank 30 or the instrument 12. When performed on theblank 30, the treated areas remain after the instrument 12 is formed asthere is no grinding or removal of material from the blank involved in atypical process of the present invention. Additional treatment may beperformed on portions of the instrument 12 after compression and/orgrinding, if desired. In other words, the treatment processes may berepeated.

In addition, other chemical surface treatments for the blank 30 may beemployed including coatings for friction reduction and/or durability.Some of these coating may include titanium nitride coating, tungstencarbide coatings, diamond-like carbon coatings, chromium coating,calcium immersion, and others for maintaining and improving thesharpness of the working surfaces 18 and to minimize the built up ofoxide layers, as noted above. The formation of titanium nitride on apassivated surface was reported to enhance the barrier to furtherNi2+ion migration, as noted in an article by L. Tan, W C. Crone /ActaMaterialia 50 (2002) 4449-4460, the content of which is herebyincorporated by reference.

Some coatings for example, DLC or titanium nitride, may have differentcolors from the blanks 30. Any change in the color of the coating on theworking portion may then act as a wear indicator.

Other treatments may also impart a different color to the treatedportions. Any change in color on the working portion may also act as awear indicator.

Further, a treatment process having a sequence of first reducing theoxide layer prior to drawing, then add treatments such aselectro-polishing, anodizing, coatings including various coatingsmentioned before, and drawing again, may be used.

In one embodiment, the instrument 12 of the present invention may have ahandle 25 at the proximal end 16 a of the shank 16 for manualmanipulation, as exemplified in FIG. 5. In another embodiment, theinstrument 12 may have a handle 25 that is adapted for attachment to amechanical handpiece, for example, a rotary or vibratory handpiece, asexemplified in FIGS. 5 a and 5 b. The handle 25 may be attached bycrimping, by an adhesive, or combinations thereof.

When adapted for rotation by means of a mechanical handpiece, the speedof rotation may be at any conventional level up to a level of about 2000to about 3,000 rpm. This is possible because of the short workingportion 22 and smaller areas of contact between the working surfaces 18and the canal walls. This is an improvement over the traditionalinstruments having a working portion along almost the entire length ofthe instrument.

The handle 25 may be attached by crimping, by an adhesive, orcombinations thereof. Surface modification such as roughening, made bycoating, sandblasting, or chemical modification made by chemicaletching, anodizing or ion implantation on or coating of the proximal endof the non-working shank either macroscopically or microscopically,depending on the treatment, may aid in the attachment of the shank to ahandle 25, as shown in FIGS. 5, 5 a and 5 b, result in the increase ofthe attachment strength of the shank 16 to the handle 25, and decreasingthe chances of separation between the handle 25 and the instrument 12during operation, as discussed further.

This improvement in attachment also enables the instrument 12 to berotated at the higher speeds with lower incidences of detachment betweenthe instrument 12 and the handle 25.

When the attachment strength between the handle 25 and the instrument 12is increased, any breakage, if it happens, may be more likely to occurat any weak points generated during the manufacturing process, ratherthan the separation between the handle 25 and the proximal end 16 a ofthe instrument 12.

In one embodiment, to increase the likelihood that such breakage mayoccur along the shank portion 16 rather than at the transition betweenthe working surface 22 and the pilot portion 10, or the working portion22 and the distal end of the shank 16 b, the shank 16 may be tapered,such as exemplified in FIG. 3 d, so that any weak point may more likelyto be towards the proximal end 16 a of the shank 16, and any brokenparts if lodged in the canal, may be more easily removed.

In FIG. 3 d, the proximal end 16 a of the shank 16 has a smallerdiameter than the distal end 16 b and the transition between the distalend 16 b of the shank 16 and that distal end 24 of the working portion22 is gradual and smooth, reducing or minimizing any stress that may becreated by the stamping process.

In another embodiment, if desired, the shank 16 may also be ground tohave a portion 16 c having a reduced circumferential span or diameter,as shown in FIG. 3 c. This reduced diameter portion 16 c may take theshape of a groove (U-shaped) or a notch (V-shaped). In one aspect, thisreduced diameter portion 16 c provides a predictable break point, incase the instrument 12 encounters some blockage in the canal thatimpedes its cutting action such that the instrument 12 does not break inthe tooth, but at the reduced diameter portion 16 c for easier retrievalfrom the tooth. In one aspect, this reduces the chance of having abroken piece that may be lodged deep within the canal of the tooth. Inanother aspect, in addition to serving as a predetermined weaknesspoint, the reduced diameter portion 16 c may also be adjusted to serveas a depth of cut indicator.

Any surface treatments on the working portion may also lead to bettercutting efficiency. This may also lower the degree of discomfort for thepatient.

A similar process and apparatus as exemplified above may be used for themanufacturing of a group of a set of instruments 12. In one embodiment,each blank 30 in the group has a different circumferential span ordiameter may be used to make one instrument 12 having a working portion22 having one circumferential span that is different from all otherinstruments 12 in the group and set. The thickness of the workingportion 22 may be substantially the same as that of other instruments 12in the group, such as exemplified in FIG. 4, discussed above.

In another embodiment, each blank in the group having an identicalcircumferential span may be used to make one instrument 12 having aworking portion 22 that is different from all other instruments 12 inthe group, such as exemplified in FIG. 4 a, also discussed above. Thisprocess has the advantage of stocking only one size of starting blanks30 for making each instrument 12 in the set having a different maximumcircumferential span, saving material and process cost.

In prior art, endodontic instruments 12 were ground into the desiredshape. This grinding process is time consuming, requires many proceduralsteps and requires the use of very specialized, expensive machinery.This grinding process also generates imperfections and flaws on thesurface of the finished working portion. These imperfections and flawsmay lead to premature failure, increasing the risk to the patient,reducing the instrument's useful life and causing it to be moreexpensive for the dentist and the patient.

The present method substantially eliminates the grinding process exceptfor the pilot portion 10, if grinding is the chosen process. The shank16 may be made without any grinding process and is therefore not marredthrough the manufacturing process. The instrument's fatigue life may beextended because the surface of the shank 16 substantially kept in itsoriginal state as that of the blank 30. Finally, this simplified formingprocess allows for less complex, less specialized equipment and lessexpensive equipment to be used for manufacturing, such as equipmentuseful for making drill bits, as exemplified above. The time tomanufacture any instrument is reduced.

The working portion 22 of the instrument 12 of the present invention maytypically be very narrow and sharp for increasing the cuttingefficiency. For example, a flattened working portion 22 may typically bemade very thin, thus reducing the surface area contact of the blade withthe root canal walls, as noted before. These thin blades, for example,typically from 0.01 mm to 1.00 mm thick, more for example, from 0.05 mmto 0.25 mm thick, also allows for more space for the previously cutmaterial to reside before being irrigated and suctioned from the canal.When compared to prior art, this extra space may also help to reduce theloss of cutting efficiency that the cut material often causes byinterfering with the cutting action of the blades. Thus, thin blades notonly increase cutting efficiency, but also reduce torsional stress onthe shank 16, which stress twisting along the longitudinal axis of theshank 16 may be a primary cause of premature instrument breakage.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theinvention in its broader aspects. Therefore, the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of the inventions. The matter set forth in theforegoing description and accompanying drawings is offered by way ofillustration only and not as a limitation. The actual scope of theinvention is intended to be defined in the following claims when viewedin their proper perspective based on the prior art.

1. A method for manufacturing a set of endodontic instruments, each ofsaid instruments having a non-working shank portion, a working portion,and a pilot portion, the method comprising: providing a set of blankshaving identical circumferential spans; positioning and compressing atleast a portion of said blank adjacent a die having walls defining atleast partially the shape-and circumferential span of the workingportion, said compressing is of sufficient force to deform said portionof said blank in contact with said walls into a shape reflecting saidwalls to form the working portion; forming the pilot portion adjacentthe working portion; wherein the shank portion of each of theinstruments in the set has a longitudinal axis and is of substantiallythe same circumferential span of the blank and each working portion hasa different circumferential span from the blank.
 2. The method of claim1 wherein said working portion comprises an average thickness and eachworking portion of one instrument in the set has a different averagethickness from the working portion of the other instruments in the set.3. The method of claim 1 further comprising treating at least a portionof each of the instruments comprising at least a portion of the shank,the working portion, the pilot portion or combinations thereof.
 4. Themethod of claim 3 further comprises attaching said treated portion to ahandle.
 5. The method of claim 1 wherein said working portion comprisesprojecting sections extending outwardly from the shank portion;projecting sections in one plane; projecting sections twisting not morethan 359° about the longitudinal axis of the shank; projecting sectionsthat are non-intersecting; or combinations thereof.
 6. The method ofclaim 3 wherein said treating comprises coating, sandblasting,anodizing, ion implantation, etching, electro-polishing, heat setting,cryogenic treatment, or combinations thereof.
 7. The method of claim 3wherein said treating is performed after the instrument has been formed,prior to the compression process, or during the manufacturing of theblank.
 8. The method of claim 1 wherein said working portion comprisesat least two projection sections.
 9. The method of claim 1 wherein saidworking portion comprises at least four projecting sections.
 10. Themethod of claim 1 wherein said pilot portion pilot portion comprisessubstantially non-cutting portions, abrasive surfaces or combinationsthereof.
 11. A method for manufacturing a set of endodontic instruments,each of said instruments having a non-working shank portion, a workingportion and a pilot portion, the method comprising: providing a set ofblanks having varying circumferential spans; positioning and compressingat least a portion of each said blank adjacent a die having wallsdefining at least partially the shape and circumferential span of theworking portion, said compressing is of sufficient force to deform saidportion of said blank in contact with said walls into a shape reflectingsaid walls to form the working portion; and forming the pilot portionadjacent the working portion; wherein each of said blank in the set hasa circumferential span substantially smaller than the circumferentialspan of the working portion and substantially the same as thecircumferential span of the non-working shank of each instrument in theset and each instrument in the set having a working portion with apredetermined circumferential span that is different from that of anyother instrument in the set.
 12. The method of claim 11 wherein thecompression force is adjusted so that the thicknesses of the workingsurfaces in the set of instruments are substantially the same.
 13. Themethod of claim 11 wherein said working portion comprises projectingsections extending outwardly from the shank portion; projecting sectionsin one plane; projecting sections twisting not more than 359° about thelongitudinal axis; projecting sections that are non-intersecting; orcombinations thereof.
 14. The method of claim 11 further comprisingtreating at least a portion of each of the instruments comprising atleast a portion of the shank, the working portion, the pilot portion orcombinations thereof.
 15. The method of claim 14 wherein said treatingcomprises coating, sandblasting, anodizing, ion implantation, etching,electro-polishing, heat setting, cryogenic treatment, or combinationsthereof.
 16. A set of endodontic instruments, each comprising: arelatively short working portion having a proximal end and a distal end;a pilot portion adjacent the proximal end of the working portion; and aflexible shank portion adjacent the distal end of said working portion,said shank portion having a longitudinal axis, a distal end and aproximal end, at least a portion of the shank portion has asubstantially smaller average circumferential span than the workingportion, and a different circumferential span from that of otherinstruments in the set; wherein the thickness of each of the workingportions in the set is substantially the same as that of others in theset, and the circumferential span of one working portion is differentfrom that of others in the set.
 17. The instrument of claim 16 whereinat least a portion of each of the instruments including the shank, theworking portion, the pilot portion or combinations thereof has beentreated.
 18. The instrument of claim 16 wherein each of said workingportions comprises at least one projecting section, said projectionsection does not twist about the longitudinal axis of more than 359degrees; does not intersect any other projection of the same instrument;or combinations thereof.
 19. The instrument of claim 16 wherein saidworking portion is flat.
 20. The instrument of claim 16 wherein saidworking portion comprises at least one projection lying substantially ina plane of the flat working portion.
 21. The instrument of claim 16wherein said instrument comprises a handle attached to the distal end ofthe shank portion.
 22. The instrument of claim 16 wherein said pilotportion comprises substantially non-cutting portions, abrasive surfacesor combinations thereof.
 23. A method for manufacturing a set of groupsof endodontic instruments having a shank portion, a working portion anda pilot portion, comprising: providing a set of groups of blanks, eachgroup of blanks having a different circumferential span from othergroups in the set; positioning and compressing at least a portion ofeach of said blank adjacent a die having walls defining at leastpartially the shape and circumferential span of the working portion,said compressing is of sufficient force to deform said portion of saidblank in contact with said walls into a shape reflecting said walls toform the working portion; and forming the pilot portion adjacent theworking portion; wherein each said working portion has a circumferentialspan substantially larger than the circumferential span of the blankfrom which it is made, and the working portion of one instrument in thegroup has a different circumferential span and thickness from the othersin the same group.
 24. The method of claim 23 wherein the thickness ofthe working portion of one instrument in one group is the same as thatof an instrument in another group.
 25. The method of claim 23 whereinthe thicknesses of the working portions in the set are different. 26.The method of claim 23 wherein the number of groups is fewer than thenumber of instruments in the set.
 27. The method of claim 23 furthercomprising treating at least a portion of each of the instrumentscomprising at least a portion of the shank, the working portion, thepilot portion or combinations thereof.
 28. The method of claim 27wherein said treating is performed after the instrument has been formed,prior to the compression process, or during the manufacturing of theblank.
 29. The method of claim 23 wherein said pilot portion pilotportion comprises substantially non-cutting portions, abrasive surfacesor combinations thereof.
 30. A set of groups of endodontic instruments,each instrument comprising: a relatively short working portion having aproximal end and a distal end; a pilot portion adjacent the proximal endof the working portion; and a flexible shank portion adjacent the distalend of the working portion, said shank portion having a longitudinalaxis, at least a portion of the shank portion has a substantiallysmaller average circumferential span than the working portion, and has adifferent circumferential span from that of instruments in other groups;wherein the thickness and circumferential span of one of the workingportions in one group is different from those of others in the group.31. The instrument of claim 30 wherein said at least a portion of eachof the instruments including the shank, the working portion, the pilotportion or combinations thereof has been treated.
 32. The instrument ofclaim 30 wherein said working portion comprises projecting sectionsextending outwardly from the shank portion; projecting sections in oneplane; projecting sections twisting not more than 359° about thelongitudinal axis of the shank; projecting sections that arenon-intersecting; or combinations thereof.
 33. The instrument of claim32 wherein said working portion comprises at least two projectionsections.
 34. The instrument of claim 30 wherein the thickness of theworking portion of an instrument in one group is the same as aninstrument in another group.
 35. The instrument of claim 30 wherein thethickness of the working portion of an instrument in one group is thesame as an instrument in every other group.
 36. The instrument of claim30 wherein the thickness of the working portion all instruments in theset is different.
 37. The instrument of claim 31 further comprises ahandle attached to the treated portion of the shank portion.